Recently, highly-functional portable phones called smartphones have been widely used. The smartphones, which have not only a telephone function but also a network terminal function for e-mails, a browser, and the like, are highly-usable portable-type communication terminals that can access various resources by being connected to a network such as the Internet whenever required.
The smartphones are highly usable as described above, but have defects that the battery lives are short. This is because the smartphones are highly functional compared with conventional portable phones and therefore the usage frequencies thereof tend to be high.
Most of the electric power of a portable terminal device such as a smartphone is used by the back-surface light source (so-called backlight) of its liquid crystal display panel. Therefore, when not operated for “a predetermined amount of time”, the portable terminal generally enters a so-called power-saving state (also referred to as a standby state) where the backlight is turned off. The portable terminal returns from the power-saving state to a normal state (a state where the backlight is on) in response to a pressing operation performed on a physical button such as a power switch. Hereinafter, the above-described predetermined amount of time will be referred to as “power-saving transition time” for convenience of explanation.
The power-saving transition time is a constant value determined in advance or a variable value that can be set by a user. The counting of the power-saving transition time is restarted every time a user operation is performed. Accordingly, the transition to the power-saving state is made when an elapsed time from a preceding user operation reaches the power-saving transition time. For example, in a configuration where the power-saving transition time is two minutes, the backlight is turned off for a transition to the power-saving state two minutes after a preceding user operation.
However, in such a measure for electric-power saving, the power-saving transition time is a “fixed value” that is a constant value (even a variable value that can be set by a user is treated as a fixed constant value after being set). Therefore, there is a defect that unnecessary electric power is inevitably consumed until the power-saving transition time elapses (two minutes in the above-described example). In this regard, in many smartphones, the power-saving transition time can be set by the users. Therefore, the above-described defect can be solved by shortening the power-saving transition time from, for example, two minutes to one minute or to several tens of seconds or shorter. However, on the other hand, when the power-saving transition time is shortened, a situation where the backlight is turned off while the user is viewing a screen occurs easily, which causes a new defect that the usability is deteriorated.
Therefore, a technique is required by which the power-saving transition time can be dynamically changed in accordance with the usage situation of the smartphone.
Examples of related techniques capable of dynamically changing the power-saving transition time include a technique where power-saving control (such as backlight turn-off: the same applies hereafter) is started comparatively late when key operations are slow, and is started comparatively early when key operations are fast in accordance with the speeds of key operations (fast key operation, slow key operation) by each user (see Patent Document 1 described below); a technique in which, if a battery remaining amount is low when data is to be downloaded from a network, the download is not executed (see Patent Document 2 described below); and a technique where a table is provided which stores power-saving setting information, such as the turning-off of a backlight, for each section and, when power-saving control is to be performed, the power-saving settings of the sections including the backlight are collectively performed by reference to the table (see Patent Document 3 described below).